Process for the continuous production of neopentyl glycol

ABSTRACT

A neopentyl glycol having a purity of 98% or more is produced continuously by a process comprising the steps of: conducting an aldol condensation of isobutyraldehyde with an aqueous formaldehyde solution containing methanol in an amount of 0.1 to 15 wt % in the presence of a tertiary alkylamine catalyst; extracting the condensation product mixture with octanol; distilling the extract; hydrogenating the distillation product; extracting the hydrogenation product mixture with water; and subjecting the extract to distillation.

FIELD OF THE INVENTION

The present invention relates to a process for the continuous productionof high-purity neopentyl glycol.

BACKGROUND OF THE INVENTION

Neopentyl glycol (2,2-dimethyl-1,3-dihydroxypropane) is a whitecrystalline material widely used in the production of various industrialchemicals such as saturated and unsaturated polyesters, alkyl andpolyurethane resins, powdered paints, synthetic lubricants,plasticizers, fiber processing agents and the like.

Neopentyl glycol is typically produced by an aldol condensation ofisobutyraldehyde with formaldehyde, followed by hydrogenation over ametal catalyst, typically a nickel catalyst, as shown in the followingReaction Scheme:

U.S. Pat. No. 3,808,280 discloses a process for producing neopentylglycol by carrying out the aldol condensation reaction in the presenceof a tertiary amine catalyst. This method has, however, the problem thatthe tertiary amine catalyst reacts with organic acids, generated viaCannizzaro reaction of aldehydes during the condensation process, toform salts. Such salts deactivate the metal catalyst used in thesubsequent hydrogenation and decompose the aldol condensation productduring the process of distillation at a high temperature, thus loweringthe yield of the desired neopentyl glycol.

Accordingly, when an amine catalyst is employed in the condensationprocess, it is required to remove most of the organic acid by-productsfrom the condensation products.

On the other hand, U.S. Pat. No. 4,885,515 discloses a process forhydrogenating the aldol condensation product under a high-temperature,high-pressure condition using a copper chromite catalyst containingmanganese, instead of a conventional nickel catalyst. However, thismethod is hampered by the problems of catalyst deactivation and anincreased equipment cost due to the requirement of a severe reactioncondition.

The product mixture obtained after the aldol condensation may containsuch by-products as isobutyl aldoxane and neopentyl glycol isobutyrate,in addition to the above-mentioned organic acids. When directlyintroduced to the hydrogenation step, said by-products convert toisobutanol and trimethylpentanediol (2,2,4-trimethyl-1,3-pentanediol),respectively, the latter having a boiling point similar to that ofneopentyl glycol. This compound is thus difficult to separate fromneopentyl glycol.

Accordingly, in order to obtain neopentyl glycol in a highly pure form,it is required to remove the above-mentioned by-products, as well as theremaining aldol condensation catalyst and unreacted reactants, prior tothe hydrogenation step.

Crude neopentyl glycol obtained after the hydrogenation step typicallycontains trimethylpentanediol and neopentyl glycol monohydroxypivalateas by-products, which are difficult to separate from neopentyl glycol bysimple distillation, due to similar boiling points thereof.

Many methods have been attempted to purify the crude neopentyl glycol,and these include solvent extraction, vacuum distillation andcrystallization methods. U.S. Pat. No. 2,895,996 discloses a process forthe purification of crude neopentyl glycol by conducting saponification,followed by sublimation, which exploits the fact that neopentyl glycolis easily sublimable. However, this method is not commercializable dueto the requirement that a low temperature must be maintained at the topof the sublimation apparatus.

Further, U.S. Pat. No. 4,935,555 suggests a method of distilling crudeneopentyl glycol by using a membrane distillation apparatus undervacuum. However, this method requires expensive equipments, and gives alow yield of neopentyl glycol.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide aneconomical, commercializable process for continuously producing highlypure neopentyl glycol.

In accordance with an aspect of the present invention, there is provideda process for the production of neopentyl glycol which comprises:

(a) reacting isobutyraldehyde with an aqueous formaldehyde solutioncontaining methanol in an amount ranging from 0.1 to 15 wt % in thepresence of a tertiary alkylamine catalyst to obtain an aldolcondensation product mixture containing hydroxypivaldehyde;

(b) extracting the condensation product mixture with an organic solventto produce a first organic phase mixture containing hydroxypivaldehydeand a first aqueous phase mixture;

(c) distilling the first organic phase mixture obtained in step (b) toobtain a low-boiling compound mixture containing materials havingboiling points lower than that of hydroxypivaldehyde, and a secondorganic phase mixture;

(d) hydrogenating the second organic phase mixture obtained in step (c)in the presence of a nickel catalyst to obtain a hydrogenation productmixture containing neopentyl glycol;

(e) extracting the hydrogenation product mixture with water to obtain asecond aqueous phase mixture containing neopentyl glycol and a thirdorganic phase mixture;

(f) subjecting the second aqueous phase mixture obtained in step (e) toan azeotropic distillation to obtain a distillation product which is amixture of neopentyl glycol and water as well as a distillation bottomproduct; and

(g) distilling the mixture of neopentyl glycol and water obtained instep (f) to obtain neopentyl glycol.

BRIEF DESCRIPTION OF DRAWING

The above and other objects and features of the present invention willbecome apparent from the following description, taken in conjunctionwith the accompanying drawing, wherein:

FIG. 1 is a schematic flow diagram showing a process for the continuousproduction of pure neopentyl glycol in accordance with a preferredembodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

A. Condensation

As the first step of the inventive process for the production ofneopentyl glycol, isobutyraldehyde is reacted with an aqueousformaldehyde solution in the presence of a tertiary alkylamine catalystto provide an aldol condensation product mixture containinghydroxypivaldehyde.

The aqueous formaldehyde solution employed in the aldol condensation ofthe present invention comprises methanol in an amount of 0.1 to 15%,preferably 0.1 to 5% by weight. Further, isobutyraldehyde may beemployed in an amount ranging from 1.0 to 1.3 moles per 1 mole offormaldehyde employed. The tertiary alkylamine employed as a catalystmay be preferably trialkylamine and may be employed in an amount rangingfrom 0.03 to 0.06 mole per 1 mole of formaldehyde employed.

The condensation process may be preferably conducted at a temperatureranging from 70 to 90° C. and for a period ranging from 1 to 3 hours.

B. Purification of Hydroxypivaldehyde by Extraction and Distillation

The condensation product mixture is then subjected to an extraction stepto recover hydroxypivaldehyde therefrom. The extraction may be conductedcounter-currently by adding a water-immiscible organic solvent to thecondensation product mixture at a temperature ranging from 40 to 70° C.In this counter-current extraction step, hydroxypivaldehyde istransferred from the aqueous condensation product phase to the organicphase.

The water-immiscible organic solvent which may be employed in thepresent invention include C₆₋₁₈ organic solvents, preferably aliphaticalcohols, most preferably octanol; and it may be employed in an amountranging from 0.3 to 4 times the weight of hydroxypivaldehyde employed.

In addition to the water-immiscible organic solvent, water may beemployed in an amount of 1 to 2 times the weight of hydroxypivaldehydeintroduced to the extraction step, for the purpose of effective removalof water soluble by-products present in the condensation productmixture, e.g., organic acids and triethylamine salts thereof.

Subsequently, the organic phase extract containing hydroxypivaldehyde isdistilled to separate materials having boiling points lower than that ofhydroxypivaldehyde, e.g., isobutyraldehyde, triethylamine and water. Thedistillation bottom entrained hydroxypivaldehyde at a recovery rate of99% or more.

The mixture of low-boiling materials obtained above may be sent to anextractive distillation step in order to recover triethylamine andisobutyraldehyde. In this extractive distillation step, the aqueousphase containing the condensation by-products obtained in the extractionstep is combined with the mixture of low-boiling materials recovered inthe distillation step, and the materials recovered in theextractive-distillation step may be recycled to the condensation step.

C. Hydrogenation

Hydroxypivaldehyde obtained as described previously is subsequentlyhydrogenated in the presence of a nickel catalyst to produce crudeneopentyl glycol. The nickel catalyst may be a Raney nickel catalystcomposed of Ni 85-90 wt %, Al 8-12 wt %, Mo 1-4 wt % and Fe 0.1-0.8 wt%; and the catalyst may be employed in an amount ranging from 2 to 10%by weight based on the weight of hydroxypivaldehyde introduced. Thetemperature and pressure employed in the hydrogenation step may rangefrom 120 to 180° C., preferably 140 to 160° C., and from 100 to 1,500psig, preferably 700 to 1,000, respectively.

In order to enhance the gas-liquid contact in the hydrogenation process,a part of the hydrogenation product mixture may be recycled to thehydrogenation step. The reactor which may be employed for this purposeis a loop-type reactor having a nozzle located at the top, which enablesrecycling of a part of the product at a high speed.

If desired, the hydrogenation product mixture containing the crudeneopentyl glycol may be subjected to a saponification step prior to theneopentyl glycol extraction step described below. In the saponificationstep, neopentyl glycol precursors such as neopentyl glycolmonohydroxy-pivalate present in the hydrogenation product mixture may beconverted to neopentyl glycol. The saponification step is conducted by aconventional method using an alkali such as sodium hydroxide.

D. Purification of Neopentyl Glycol by Extraction and Distillation

The hydrogenation product mixture containing neopentyl glycol issubsequently extracted with water. In this extraction step, thehydrogenation product mixture and water are contacted countercurrently,wherein water may be employed in an amount ranging from 0.5 to 4 times,preferably 1 to 1.5 times the weight of neopentyl glycol. The extractionmay be conducted at a temperature ranging from 10 to 50° C. Inaccordance with the present invention, neopentyl glycol is transferredto an aqueous phase, but by-products remain in the organic phase.Therefore, in accordance with the present invention, neopentyl glycolcan be easily isolated from by-products at an ambient temperature.

The extract obtained in this extraction step, an aqueous phase mixture,comprises neopentyl glycol and water in a weight ratio of about 4:6 toabout 9:1.

Thereafter, the aqueous phase mixture containing neopentyl glycol issubjected to an azeotropic distillation process. In this step, a mixtureof neopentyl glycol and water is distilled to separate and remove smallamount of impurities, e.g., salts of organic acids. In order to increasethe efficiency, the azeotropic distillation process may be conductedusing a column packaged with materials which are capable of trappingsaid impurities.

The mixture of neopentyl glycol and water thus evaporated is thendirectly introduced in the form of a vapor to a distillation stepwherein it is distilled to separate water and obtain pure neopentylglycol. Water thus separated may be recycled to the water extractionstep.

Alternatively, the azeotropic distillation and the final distillationsteps may be integrated into one step. In this case, the mixture ofneopentyl glycol and water may be preferably sparged to the bottom of anintegrated distillation column.

On the other hand, the azeotropic distillation residue containingorganic acid impurities may also contain some residual neopentyl glycoland this fraction may be extracted with an organic solvent, preferablyoctanol, in a countercurrent mode, for the purpose of recoveringneopentyl glycol remaining therein. This extraction procedure may bepreferably conducted using a multi-stage extraction apparatus in acontinuous manner. The organic phase extract containing neopentyl glycolmay then be recycled to the water extraction step.

In accordance with the present invention, the rate of recovery ofneopentyl glycol produced in the hydrogenation step may reach 98% ormore. The pure neopentyl glycol product thus obtained may be formed intoflakes using a conventional flaker or may be mixed with water under apressure of 0.1 to 5 kg/cm² to form an aqueous solution.

PREFERRED EMBODIMENT OF THE INVENTION

In accordance with a preferred embodiment of the present invention, pureneopentyl glycol may be continuously produced as follows:

Specifically, referring to a schematic flow diagram shown in FIG. 1, anaqueous solution of formaldehyde is continuously fed via pipe (2), andisobutyraldehyde and a tertiary amine such as triethylamine arecontinuously fed via pipes (1) and (3), respectively, to aldolcondensation reactor (10) where an aldol condensation product mixturecontaining crude hydroxypivaldehyde is obtained.

The condensation product mixture is then led from the top of reactor(10) to the upper region of extractor (20) via pipe (11) while octanolis introduced separately via pipe (4) to the lower region of extractor(20) wherein hydroxypivaldehyde is transferred from the condensationproduct mixture to the organic phase. At this time, water may be addedto extractor (20) together with octanol in order to enhance the removalof water-soluble impurities, if necessary.

The organic phase containing crude hydroxypivaldehyde is transferredfrom the upper region of extractor (20) via pipe (21) to distillationcolumn (30) wherein low boiling materials, such as excessisobutyraldehyde, triethylamine and water, are removed.

The organic phase containing purified hydroxypivaldehyde is thencontinuously drawn from the bottom of column (30) and fed via pipe (32)to hydrogenation reactor (50), while the mixture of low boilingmaterials leaving the top of column (30) is introduced via pipe (31) toextractive distillation column (40) to be treated together with theaqueous phase mixture introduced from the bottom of column (20) via pipe(22).

In extractive distillation column (40), low boiling materials arerecovered and recycled via pipe (41) to reactor (10) for reuse, and theremaining solution is discarded via pipe (42).

In hydrogenation reactor (50), the organic phase mixture containingpurified hydroxypivaldehyde contacts with hydrogen gas fed separately inthe presence of a Raney nickel catalyst to produce a hydrogenationproduct mixture containing crude neopentyl glycol. At this time, a partof the hydrogenation product mixture may be recycled to hydrogenationreactor (50), using a nozzle positioned at the top and a high-speedpump, in order to enhance the liquid-gas contact.

The hydrogenation product mixture is then transferred via pipe (51) tosaponificator (60) wherein it mixes with sodium hydroxide fedseparately, and neopentyl glycol esters of, e.g., hydroxypivalic acidundergo hydrolysis to recover neopentyl glycol.

The output from saponificator (60) is then introduced via pipe (61) tothe bottom region of extractor (70) wherein it meets countercuzrentlywith water, freshly introduced or recycled from distillation column (90)to the upper region of extractor (70), wherein neopentyl glycol istransferred from the organic phase to the aqueous phase.

The organic phase is released via pipe (71) while the aqueous phase isdrained out from the bottom of extractor (70) and then spargedcontinuously to the lower region of azeotropic distillation column (80)via pipe (72), wherein a mixture of neopentyl glycol and water isseparated from organic salt impurities. A part of the upper region ofcolumn (80) is packaged with materials capable of preventing the passageof the organic salt impurities.

The vapor mixture of neopentyl glycol and water is continuouslytransferred from the top of column (80) to distillation column (90) viapipe (81). Water condensed at the top of column (90) is recycled toextractor (70) via pipe (91), while the desired pure neopentyl glycol isrecovered as a bottom product of distillation column (90).

The azeotropic distillation residue containing organic salt impuritiesas well as some residual amount of neopentyl glycol is taken out fromthe bottom of column (80) and introduced via pipe (82) to the upperregion of extractor (100), where it contacts countercurrently an organicsolvent which is separately fed to the lower region of extractor (100)via pipe (5). The organic phase containing recovered neopentyl glycol isdrawn from the upper region of extractor (100) and then recycled to thelower region of extractor (70) via pipe (101). The aqueous phase drainedfrom the bottom of extractor (100) is discarded via pipe (102).

As described previously, in accordance with the present invention,neopentyl glycol may be produced in a high purity by way of purifyingcrude hydroxypivaldehyde or neopentylglycol by a series of anextraction, distillation and extractive distillation process.

The following examples are only provided for the purposes ofillustrating certain aspects of the present invention; they are not tobe construed as limiting the scope of the present invention in any way.

EXAMPLE 1 Production of hydroxypivaldehyde

A 20 liter reactor equipped with a stirrer was continuously fed withisobutyraldehyde, 38% formaldehyde aqueous solution (methanol content0.3% ) and triethylamine at rates of 46.8 g/min, 42.2 g/min, and 2.6g/min, respectively. The reactor was maintained at 70 to 90° C. under anitrogen pressure of 10 to 40 psi.

The residence time was adjusted at 1 hour and the condensation productmixture containing crude hydroxypivaldehyde was removed from the reactorat a rate of 91.6 g/min.

This condensation product mixture having the composition shown in Table1 was introduced continuously to the upper region of a multi-stageextractor, where the condensation product stream contacts an octanolstream fed separately to the lower region of the extractor. Thiscounter-current extraction of the condensation product mixture withoctanol removes most of trimethylamine salts of organic acids andunreacted reactants from the condensation product stream containinghydroxypivaldehyde.

The multi-stage extractor having a diameter of 60 mm and 30 stages wasequipped with a stirrer and a water jacket for maintaining a constanttemperature of 30 to 70° C. The rate of stirring in the extractor was 80rpm. No significant loss of hydroxypivaldehyde was observed in thisextraction step, and the composition of the crude hydroxypivaldehydestream exiting the extractor is shown in Table 1.

The crude hydroxypivaldehyde stream from the extractor was thenintroduced to a glass distillation column having a diameter of 50 mm and15 stages (constructed by Oldshaw, Shott, Germany) and distilled torecover low boiling point materials such as isobutyraldehyde andtriethylamine at a column bottom temperature of 80 to 110° C. under apressure of 400 to 700 mbar.

An aqueous distillate containing the low boiling point materialsrecovered from the top of the distillation column was recycled to thealdol condensation reactor, while a mixture containinghydroxypivaldehyde having the composition shown in Table 1 was recoveredfrom the bottom of the column.

TABLE 1 After After condensa- After distilla- tion step extraction tionstep (wt %) step (wt %) (wt %) Methanol  0.5  0.25 — Isobutanol — — —Water 28.9 10.8   5.88 Octanol — 26.69 30.68 Isobutyraldehyde  7.4  6.69 0.98 Triethylamine and  4.6  2.41  0.54 organic saltsHydroxypivaldehyde 52.6 47.81 56.33 Neopentylglycol  1.2  1.08  0.92Neopentylglycol  3.0  2.73  4.22 ester Others  1.8  1.54  0.45

EXAMPLE 2 Production of crude neopentyl glycol

A product mixture containing hydroxypivaldehyde obtained as in Example 1was continuously introduced at a rate of 13 g/min to a 2 liter autoclaveequipped with a stirrer and the hydrogenation was carried out to producea mixture containing crude neopentyl glycol. The hydrogenation wasconducted at 150° C. under a hydrogen pressure of 1,000 psi for 26 hoursin the presence of a Raney nickel catalyst in an amount of 6% by weightbased on the weight of hydroxypivaldehyde employed. No significantcatalyst deactivation was observed during a 80 hour run.

The changes in the composition before and after the hydrogenation stepare shown in Table 2.

TABLE 2 Before After Hydrogenation hydrogenation step (wt %) step (wt %)Methanol 0.25  0.37 Isobutanol 0.06  2.02 Water 6.31  6.23 Octanol 35.1734.72 Isobutyraldehyde 2.29  0.35 Triethylamine 1.11  1.10Hydroxypivaldehyde 48.45 — Neopentylglycol 3.95 52.96 Neopentylglycol1.54  1.52 ester Trimethylpentanediol 0.74  0.73 Others 0.13 —

EXAMPLE 3 Extraction of neopentyl glycol

A hydrogenation product mixture containing crude neopentyl glycolobtained as in Example 2 was continuously introduced to the lower regionof an extractor at a flow rate of 215 g/min while water was continuouslyintroduced to the upper region of the extractor at a flow rate of 175g/min. In this counter-current extraction step, neopentyl glycol in thehydrogenation product mixture was transferred to the aqueous phase.

The extractor was made of glass and had an inner diameter of 60 mm,height of 3 m and 50 stages. The extractor was a Scheibel type equippedwith a stirrer on the upper region for enhancing countercurrent contactof the hydrogenation product mixture with water. The extraction processwas conducted at 30° C. and a contact time of 25 minutes.

The aqueous phase containing neopentyl glycol was drained out from thebottom of the extractor at a flow rate of 293.8 g/min and the organicphase was fluxed from the top of extractor at a flow rate of 93.04g/min. The efficiency of the extraction was 99.2%.

The compositions of the hydrogenation product mixture introduced and theaqueous and organic streams obtained from the extraction process areshown in Table 3.

TABLE 3 Hydrogena- Aqueous tion Organic phase product phase after aftermixture extraction extraction (wt %) (wt %) (wt %) Neopentylglycol 48.8  1.17 31.88 Octanol 40.9  86.98  3.63 water  6.78  9.03 63.19 Materials— — — having low boiling temp. TMPD  0.42  0.42 0.1 HPNE 3.1 2.4 1.2*TMPD: Trimethylpentane diol *HPNE: Neopentyl glycol ester ofhydroxypivalic acid

EXAMPLE 4

A hydrogenation product mixture obtained as in Example 2 wassaponificated by the addition of NaOH, prior to the extraction stepaccording to Example 3, for the purpose of converting neopentyl glycolmonohydroxypivalate present in the hydrogenation product mixture toneopentyl glycol and sodium hydroxypivalate. Subsequently, theextraction process was conducted at 32° C. and a contact time of 30minutes.

The aqueous phase containing neopentyl glycol was recovered from thebottom of the extractor at a flow rate of 298.8 g/min and the organicphase was vent off from the top of column at a flow rate of 88.9 g/min.The efficiency of the extraction was 99.43%.

The analytical results of the saponification and extraction experimentare shown in Table 4.

TABLE 4 Aqueous Hydrogena- Organic phase tion product phase after aftermixture extraction extrac- (wt %) (wt %) tion (wt %) Neopentylglycol47.7  0.38 30.71 Octanol 38.7 89.92  2.35 water 10.8 8.9 66.04 Materialshaving — — — low boiling temp. TMPD  0.4 0.6 0.1 HPNE  0.1 0.2 — Sodiumsalt  2.3 — 0.8

As shown in Table 4, the levels of TMPD and HPNE in the aqueous extractare greatly reduced by the inclusion of a saponification step.

EXAMPLE 5 Purification of neopentyl glycol

An aqueous phase obtained after the extraction process as in Example 4was continuously introduced at a flow rate of 20 g/min to the bottom ofan azeotropic distillation column using a sparger.

The azeotropic distillation column was a 1 m long glass column having adiameter of 30 mm and it was packaged with glass raschig ring in theheight of 30 cm from the top. The top region of the column wasmaintained at 118 to 123° C. and the bottom region was maintained at 130to 135° C. The azeotropic distillation was conducted under a pressure of320 to 330 mbar.

(1) Recovery and recycling residual neopentyl glycol present in theazeotropic distillation bottom

The bottom product stream from the azeotropic distillation column wasmixed with water in a weight ratio of 1:0.6 and the resulting mixturewas continuously introduced to the upper region of a multi-stageextractor at a flow rate of 29.8 g/min. Separately, octanol wasintroduced to the lower region of the extractor at a flow rate of 37.4g/min. In this counter-current extraction conducted at 75° C., neopentylglycol was transferred to the octanol stream.

The octanol stream containing neopentyl glycol was fluxed from the topof the extractor at a flow rate of 51.4 g/min and then recycled to theextractor of Example 4. Further, the aqueous phase containing watersoluble salts was drained out from the bottom of the extractor at a flowrate of 13.1 g/min and then discarded.

The rate of recovery of neopentyl glycol originally present in thebottom product was 98.6% and 95.9% of the sodium salts was removed.

The compositions of the bottom product of the azeotropic distillationcolumn, and the products obtained at the top and the bottom of theextractor were analyzed by gas chromatography and the results are shownin Table 5.

TABLE 5 Bottom Top Bottom product of product of product of azeotropicthe the distillation extractor extractor column (wt %) (wt %) (wt %)Neopentylglycol 43.67 23.72  1.37 Water 37.61  6.10 60.38 Sodium salts18.72  1.11 38.02 Octanol — 69.08  0.23

(2) Final purification of neopentyl glycol

The product stream leaving the top of the azeotropic distillationcolumn, on the other hand, was continuously introduced to a positionbetween the 8th stage and the 12th stage of a multi-stage distillationcolumn having 15 stages. The temperature at the top region of thisdistillation column was 66 to 68° C. and the temperature at the bottomregion was 175 to 180° C. The aqueous solution was condensed at the topregion and then removed at a flow rate of 6 to 6.5 g/min while a highlypure neopentyl glycol stream was recovered at a flow rate of 13.5 to14.0 g/min at the bottom of the column.

The compositions of the aqueous phase product obtained after theextraction, and the products obtained at the top and the bottom of thedistillation column were analyzed by gas chromatography and the resultsare shown in Table 6.

TABLE 6 Aqueous phase Bottom product Top product product of obtained ofthe the after distilla- distilla- extraction tion column tion column (wt%) (wt %) (wt %) Neopentylglycol 30.81 — 99.5  Water 67.6 99.35 0.15Sodium salts 1.0 — — Octanol 0.4 0.5 0.05 TMPD 0.09 — 0.25 Others 0.1 0.15 0.05

As clearly seen from the results of Examples 1 to 5, in accordance withthe present invention, highly pure neopentyl glycol can be continuouslyand economically produced.

While the invention has been described with respect to the specificembodiments, it should be recognized that various modifications andchanges may be made by those skilled in the art to the invention whichalso fall within the scope of the invention as defined by the appendedclaims.

What is claimed is:
 1. A process for the production of neopentyl glycolwhich comprises the steps of: (a) reacting isobutyraldehyde with anaqueous formaldehyde solution containing methanol in an amount rangingfrom 0.1 to 15 wt % in the presence of a tertiary alkylamine catalyst toobtain an aldol condensation product mixture containinghydroxypivaldehyde; (b) extracting the condensation product mixture withan organic solvent to produce a first organic phase mixture containinghydroxypivaldehyde and a first aqueous phase mixture; (c) distilling thefirst organic phase mixture obtained in step (b) to obtain a low-boilingcompound mixture containing materials having boiling points lower thanthat of hydroxypivaldehyde, and a second organic phase mixture; (d)hydrogenating the second organic phase mixture obtained in step (c) inthe presence of a nickel catalyst to obtain a hydrogenation productmixture containing neopentyl glycol; (e) extracting the hydrogenationproduct mixture with water to obtain a second aqueous phase mixturecontaining neopentyl glycol, and a third organic phase mixture; (f)subjecting the second aqueous phase mixture obtained in step (e) to anazeotropic distillation to obtain a distillation product which is amixture of neopentyl glycol and water as well as a distillation bottomproduct; and (g) distilling the mixture of neopentyl glycol and waterobtained in step (f) to obtain neopentyl glycol.
 2. The process of claim1 further comprising the steps of combining the first aqueous phasemixture obtained in step (b) and the low-boiling compound mixtureobtained in step (c), subjecting the combined mixture to an extractivedistillation and recycling the extract to the condensation step (a). 3.The process of claim 1 wherein the aqueous formaldehyde solutioncomprises methanol in an amount of 0.1 to 5 wt %.
 4. The process ofclaim I wherein the organic solvent employed in step (b) is octanol. 5.The process of claim 3 wherein the organic solvent is employed in anamount ranging from 0.3 to 4 times the weight of the hydroxypivaldehydeintroduced.
 6. The process of claim 4 wherein water is further employedin an amount of 1 to 2 times the weight of hydroxypivaldehydeintroduced, together with octanol.
 7. The process of claim 1 wherein thehydrogenation step (d) is conducted at a temperature ranging from 120 to180° C. and a pressure ranging from 100 to 1,500 psig.
 8. The process ofclaim 1 wherein a part of the hydrogenation product mixture is recycledto the hydrogenation step (d) using a loop-type reactor.
 9. The processof claim 1 further comprising the step of saponificating the productmixture obtained in the hydrogenation step (d) using an alkali.
 10. Theprocess of claim 1 wherein the amount of water employed in theextraction step (e) is 0.5 to 4 times the weight of neopentyl glycolintroduced.
 11. The process of claim 1 wherein the extraction step (e)is conducted at a temperature ranging from 10 to 50° C.
 12. The processof claim 1 wherein the second aqueous phase mixture obtained in step (e)contains 10 to 60% by weight of water.
 13. The process of claim 1further comprising the step of extracting the distillation bottomproduct obtained in the azeotropic distillation step (f) with an organicsolvent to recover neopentyl glycol therefrom.
 14. The process of claim1 wherein the distillation product obtained by the azeotropicdistillation step (f) is introduced in the form of a vapor to thedistillation step (g).